1 Technical Field
The present disclosure relates to field winding type rotating electric machines.
2 Description of Related Art
Conventionally, field winding type rotating electric machines have been known which create magnetic fields through energization of a stator armature winding (see, for example, Patent Document 1 and Patent Document 2). These field winding type rotating electric machines include a stator and a rotor. The stator includes a stator core and the stator armature winding wound on the stator core. The rotor includes a rotor core and a rotor field winding wound on the rotor core. The rotor field winding is short-circuited via a diode which is a rectifying element. That is, the diode is connected to both ends of the rotor field winding.
Moreover, the above-described field winding type rotating electric machines further include an inverter circuit connected with the stator armature winding and a control circuit that controls the inverter circuit to supply electric currents, which depend on the rotational position of the rotor, to the stator armature winding. Each of the electric currents flowing in the stator armature winding is the sum of fundamental current (i.e., synchronous current), which is a current component for generating rotational torque, and excitation current that is a current component for the rotor excitation. The excitation current for the rotor excitation is harmonic current having a shorter period (or higher frequency) than the fundamental current; the excitation current has a pulsed waveform. Upon the excitation current for the rotor excitation being supplied to the stator armature winding, excitation magnetic flux crosses main magnetic poles of the rotor core, causing a voltage to be generated in the rotor field winding and thereby inducing excitation current.
As described above, to both the ends of the rotor field winding, there is connected the diode. Therefore, electric current flows only in one direction in the rotor field winding even when the excitation magnetic flux fluctuates to cause an AC voltage to be generated in the rotor field winding. The rotor core is excited in a predetermined direction to form field poles (specifically, N poles and S poles). The field flux for forming the field poles is generated by supply of the excitation current for the rotor excitation to the stator armature winding and rectification of the electric current flowing in the rotor field winding.
As above, in the rotating electric machines where the field poles are formed by having the excitation magnetic flux from the stator received by the rotor field winding and rectifying through the diode the electric current flowing in the rotor field winding, to generate rotational torque, the rotor core is excited by causing the excitation magnetic flux to cross the main magnetic poles of the rotor core. The excitation of the rotor core is realized by superimposing the pulsed excitation current on the fundamental current and thereby inducing excitation current in the rotor field winding.